Low staffing levels have prompted mental health chiefs to temporarily close the Fermoy Unit in Lynn.
Norfolk and Suffolk NHS Foundation Trust say the closure is a short-term plan while it runs a recruitment campaign.
New admissions will be forced to travel to Norwich, Great Yarmouth or Gimmingham while the existing 15 patients will remain at the Fermoy.
Current staffing level at the unit, which is based at Lynn’s Queen Elizabeth Hospital, is 31 a but should be 36 fulltime equivalents.
Chief-executive Michael Scott said no decision has been taken to permanently close the site but this was a temporary measure to ensure the safety of staff and patients.
He said: “This is a short term plan while we continue to recruit new staff to ensure we maintain safe staffing levels.
“We are working closely with West Norfolk Clinical Commissioning Group to look at a number of long term options for the unit; the safety and needs of our patients and staff will remain central to whatever decision is ultimately made.
“At NSFT we do have an enhanced recruitment programme underway and are actively looking for additional staff across both Norfolk and Suffolk.”
The CCG is seeking assurance that “appropriate” action is being taken to reinstate services.
A statement says: “We will require the trust to have a clear timescale for recruiting to the necessary posts and will be closely monitoring this.”
Trade unionist Jo Rust said there is no evidence of how temporary this closure will be.
She said: “Combined with the threatened closure of the CAB, this is a dreadful blow for Lynn. There are people out there who are suicidal, who need these services.
“How many more things are going to be closed in King’s Lynn?”
MP Sir Henry Bellingham hopes to meet with Mr Scott and had previously been told that the unit need some modernisation.
He said: “We need those beds. It is absolutely ridiculous for people to travel long distances for in patient treatment.
“At a time when incidents of mental health are growing, what Mr Scott needs to do is get a grip of the staffing issue.
“I think there is real concern over attracting psychologists and psychiatrists and other mental health workers.
“I think the health family in East Anglia could do more to promote Norfolk as an amazing place to live and work.
“There is also a chance for promotion and a very successful career here.”